The present invention relates to a push-button tuner. More particularly, it relates to improvements in a push-button tuner including a slide member which slides in a predetermined direction to interlock with a tuning core, a lock member which is movable in a direction orthogonal to the sliding direction of the slide member and which is provided with means grasping a cam member turnably supported by the lock member for placing the tuning slide member in a preset position.
FIG. 6 is a partial plan view of a prior-art push-button tuner of the specified type.
Referring to FIG. 6, a slide plate 1 is movable in the directions indicated by the arrow A to adjust the position of a core within a tuning coil, as is well understood in the art. The slide plate 1 has a plurality, such as five, V-shaped grooves 2 formed along one side edge. Adjacent the V-shaped grooves 2, there is arranged a lock slide plate 3 which can move in the direction of the arrow B orthogonal to the sliding direction A of the tuning slide plate 1.
In a predetermined position of the lock slide plate 3, a V-shaped groove 4 opening rightward as viewed in the drawing is formed. Spaced rightwardly from the groove is the point of application 6 of a lever piece 5. The fore end part of the lever piece 5 is coupled with the lock slide plate 3 at a fulcrum point 7 for the lever piece 5. The free end side of the lever piece 5 acts as a point of force 8, and a lock pin 9 movable in the direction of the arrow B is inserted near the point of force.
A cam shaft 11 which is connected to the lower surface of a cam 10 is inserted between the V-shaped groove 4 of the lock slide plate 3 and the point of application 6 of the lever piece 5. An engaging protuberance 12 projects outwardly from the fore end part of the cam 10, and it is adapted to ride in contact with walls of the groove 2 of the tuning slide plate 1. During the advance or retreat of the lock slide plate 3 it is guided by guide members 13. Both ends of the tuning slide plate 1 are respectively supported by links 14, and the tuning slide plate 1 may slide in the direction of the arrow A by the turning of the links 14.
In a state before presetting, the lock pin 9 lies in a position shown by a dot-and-dash line, while the lever piece 5 lies at a position shown by a dot-and-dash line and its point of application 6 is away from the cam shaft 11. Accordingly, the cam shaft 11 is not grasped or held tightly between the groove 4 and the point of application 6, and the cam 10 is rotatable within the groove 4.
The tuner may then be tuned to a desired channel by manual operation, and the tuning slide plate will be moved in the direction A to the position corresponding to the selected channel. The locking slide plate 3 may then be slide toward the tuning slide plate 1 and, the engaging protuberance 12 of the cam 10 abuts against the inclined wall of the groove 2 in the tuning slide plate 1 at first. When the lock slide plate 3 is further advanced, the engaging protuberance 12 is guided by the inclined wall of the groove 2 and abuts against the bottom part thereof while the cam 10 is turning. Under this state, when the lock slide plate 3 is further pushed towards the tuning plate 1, the lock pin 9 is thrust against the side of the point of force 8 of the lever piece 5, and the lever piece 5 is urged towards the groove 4 about the fulcrum 7 as indicated by a solid line, and the cam shaft 11 is tightly held within the groove 4 and the point of application 6. Thus, the positioning of the cam 10 in the turning direction is made, and the presetting operation ends.
In selecting a preset station, the lock slide plate 3 with the cam 10 held in its preset position is pushed toward the tuning slide plate 1, while the tuning slide plate is freely slidable. Then, the engaging protuberance 12 of the cam 10 comes into contact with the inclined wall of the groove 2 of the tuning slide plate 1. By pushing the lock slide plate 3 still further, the slide plate moves in the direction A until the protuberance 12 moves into the bottom of the groove 2, so that the tuning slide plate 1 is positioned in its preset position. When the lock slide plate 3 is further pushed towards the slide plate 1, the engaging protuberance 12 of the cam 10 is intensely pushed against the bottom part of the groove 2, and it does not advance any more.
As described above, when the lock slide plate 3 is pushed inwardly in the direction of the arrow B during presetting of the tuner, and selecting the preset station, the cam 10 collides with the tuning slide plate 1, whereby the sliding of the lock slide plate 3 is stopped.
In the above device, both the ends of tuning slide plate 1 are respectively supported by the links 14, and the tuning slide plate 1 is not free to retreat in accordance with the thrust of the lock slide plate 3. Therefore, when the cam 10 collides against the tuning slide plate 1 by thrusting the lock slide plate 3, large forces act on the cam 10 and the tuning slide plate 1. This sometimes results in that the cam 10 is not properly locked at a desired position or that the cam 10 having been correctly locked with effort shifts due to the strong collision against the tuning slide plate 1. For such reasons, the preset condition of the tuner may vary and the tuner is thus not very reliable.